Capsule endoscope is an in vivo imaging device which addresses many of problems of traditional endoscopes. A camera is housed in a swallowable capsule along with a radio transmitter for transmitting data to a base-station receiver or transceiver. A data recorder outside the body may also be used to receive and record the transmitted data. The data primarily comprises images recorded by the digital camera. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead of using radio-frequency transmission, lower-frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule. In another type of capsule camera with on-board storage, the captured images are stored on-board instead of transmitted to an external device. The capsule with on-board storage is retrieved after the excretion of the capsule. The capsule with on-board storage provides the patient the comfort and freedom without wearing the data recorder or being restricted to proximity of a wireless data receiver.
The images and data after being acquired and processed are usually displayed on a display device for a diagnostician or medical professional to examine. However, each image only provides a limited view of a small section of the GI tract. It is desirable to form (stitch) a single composite picture with a larger field of view from multiple capsule images. A large picture can take advantage of the high-resolution large-screen display device to allow a user to visualize more information at the same time. An image stitching process may involve removing redundant overlapped areas between images so that a larger area of the inner GI tract surface can be viewed at the same time in a single composite picture. In addition, a large picture can provide a complete view or a significant portion of the inner GI tract surface. It should be easier and faster for a diagnostician or a medical professional to quickly spot an area of interest, such as a polyp. Moreover, captured images may have, for example, 30,000 frames. It will take users more than one hour for review. An image stitching process can thus reduce frame numbers and accelerate the review procedure.
However tissues in the GI tract often deform. Also the capsule movement inside the GI track is not steady. The camera may rotate and hesitate inside the human GI tract. In addition, while the GI tract is supposedly cleaned well before administering the capsule, various objects such as food residues and bubbles may still appear in the images. Therefore, the images captured by the capsule camera are non-ideal from the image models used in various image composition or image stitching processing. It is desirable to develop methods that take into consideration of the fact that the captured images are non-ideal and improve the processing or algorithm convergence speed. For example, if a method can reliably stitch certain types of images, it would reduce the total number to be processed images. Furthermore, if another method can be developed to reliably stitch another type of images, the total number of images to be processed is further reduced.